Alternating Color Fill

I’m having a little trouble figuring out how to do an alternating color fill animation. I’m probably missing something simple. My daughter would like to theme the lights in her room to alternating red/green. I can do a red or green fill but how can I do a fill of 300 WS2812Bs where each light alternates between static red and green?

If I understand what you want correctly… just use this: